The roles of cofilin and LIM-kinase in chemotaxis of phagocytes

Cofilin是一种普遍存在的肌动蛋白结合蛋白。只有未磷酸化的cofilin结合肌动蛋白并切断或解聚丝状肌动蛋白（F-actin）， cofilin被lim激酶（cofilin的一种特异性激酶）磷酸化，成为不结合肌动蛋白的非活性形式。磷酸化的cofilin被一种特殊的磷酸酶“弹弓”去磷酸化，成为一种活性形式。最近我们报道了cofilin在吞噬细胞的超氧化物产生和吞噬中起调节作用。本研究探讨了cofilin在白细胞趋化性中的作用。白介素8（IL-8）是一种有效的生理趋化因子，可触发cofilin的快速去磷酸化和随后的再磷酸化。S3-R肽是由一种膜渗透肽和一种cofilin磷酸化位点肽组成的肽，可抑制cofilin的磷酸化。将S3-R肽引入中性粒细胞样HL-60细胞后，其趋化活性增强，而含有cofilin磷酸化位点倒置序列的对照肽则没有增强作用。PI3激酶抑制剂Wortmannin和LY294002抑制cofilin的趋化性和磷酸化转换。另一方面，cofilin的siRNA引起cofilin的下调，抑制其趋化性。这些结果表明，未磷酸化的活性cofilin在吞噬细胞的趋化过程中起关键作用，pi3激酶参与控制cofilin的磷酸化/去磷酸化周期。

Cofilin is a ubiquitous actin-binding protein. Only unphosphorylated cofilin binds actin and severs or depolymerizes a filamentous actin(F-actin) and cofilin is phosphrylated by LIM-kinase, a specific kinase of cofilin, to be an inactive form which does not bind actin. The phosphorylated cofilin is dephosphorylated by slingshot, a specific phosphatase, to be an active form. Recently we have reported that cofilin plays regulatory roles in superoxide production and phagocytosis by phagocytes. In this study, the roles of cofilin hi chemotaxis of leukocytes were investigated. Interleukin 8(IL-8), a potent physiological chemokine, triggered quick dephoshorylation and subsequent rephosphorylation of cofilin. The phosphorylation of cofilin was inhibited by S3-R peptide which consisted of a membrane-permeable peptide and a peptide of phosphorylation site of cofilin. When the S3-R peptide was introduced into neutrophil-like HL-60 cells, the chemotactic activity was enhanced while control peptide which contained an inverted sequence of phosphorylation site of cofilin did not such an enhancing effect. Wortmannin and LY294002,inhibitors of PI3 kinase, suppressed the chemotaxis and phosphorylation turnover of cofilin. On the other hand, siRNA of cofilin caused down-regulation of cofilin and inhibited the chemotaxis. Based on these results it is suggested that unphosphrylated active cofilin plays a critical role in the chemtaxis of phagocytes and PI3-kinase is involved in the control of phosphorylation/dephosphorylation cycle of cofilin.